1 files changed, 14 insertions, 0 deletions
diff --git a/py/sequence.c b/py/sequence.c
index cc31be983..0e668ea2a 100644
--- a/py/sequence.c
+++ b/py/sequence.c
@@ -34,6 +34,20 @@
 
 #define SWAP(type, var1, var2) { type t = var2; var2 = var1; var1 = t; }
 
+#if __GNUC__ < 5
+// n.b. does not actually detect overflow!
+#define __builtin_mul_overflow(a, b, x) (*(x) = (a) * (b), false)
+#endif
+
+// Detect when a multiply causes an overflow.
+size_t mp_seq_multiply_len(size_t item_sz, size_t len) {
+    size_t new_len;
+    if (__builtin_mul_overflow(item_sz, len, &new_len)) {
+        mp_raise_msg(&mp_type_OverflowError, translate("small int overflow"));
+    }
+    return new_len;
+}
+
 // Implements backend of sequence * integer operation. Assumes elements are
 // memory-adjacent in sequence.
 void mp_seq_multiply(const void *items, size_t item_sz, size_t len, size_t times, void *dest) {